We present first results of a research project that has the goal to develop an analyzer for volatile organic compounds
(VOCs) with extraordinarily high detection sensitivity and detection selectivity. Due to its high potential concerning
these two key parameters, optical spectroscopy is employed. The new detection scheme is based on photoacoustic
spectroscopy (PAS). PA detection utilizes the fact, that the excitation energy of light absorbing molecules is essentially
transferred into kinetic energy of the surrounding molecules via inelastic collisions. This causes a local pressure increase
in the absorbing gas. If the excitation source is modulated, a sound wave is generated that can be detected by a
microphone and phase-sensitively measured using a lock-in amplifier. A considerable challenge of this project is
represented by the broad and strongly overlapping absorption bands of the hydrocarbons. Discrimination of the VOCs is
possible only by using a spectrally tunable monochromatic radiation source in combination with a sophisticated data
analysis algorithm. Therefore, we apply an optical parametric oscillator (OPO) with spectral emission between 3 and
The composition and concentration of exhaled volatile gases reflects the physical ability of a patient. Therefore, a breath
analysis allows to recognize an infectious disease in an organ or even to identify a tumor. One of the most prominent
breath tests is the 13C-urea-breath test, applied to ascertain the presence of the bacterium helicobacter pylori in the
stomach wall as an indication of a gastric ulcer. In this contribution we present a new optical analyzer that employs a
compact and simple set-up based on photoacoustic spectroscopy. It consists of two identical photoacoustic cells
containing two breath samples, one taken before and one after capturing an isotope-marked substrate, where the most
common isotope 12C is replaced to a large extent by 13C. The analyzer measures simultaneously the relative CO2
isotopologue concentrations in both samples by exciting the molecules on specially selected absorption lines with a
semiconductor laser operating at a wavelength of 2.744 μm. For a reliable diagnosis changes of the 13CO2 concentration
of 1% in the exhaled breath have to be detected at a concentration level of this isotope in the breath of about 500 ppm.
Exhaled nitric oxide was of high interest in breath analyses in the past few years. After its first detection in human breath
in 1991, numerous publications uncovered the role of NO and its relation to different diseases. A strong relationship
between an asthmatic eosinophilic airway inflammation and an increased NO level is medically confirmed. In this study
a new photoacoustic detection system for nitric oxide based on a pulsed quantum cascade laser is introduced. The laser's
single mode emission provides adequate selectivity to differentiate NO from other molecules in the sample. The
demonstrated detection sensitivity allows in principle an application of the new system as diagnostic tool for asthma.
Medical breath tests are well established diagnostic tools, predominantly for gastroenterological inspections, but also for
many other examinations. Since the composition and concentration of exhaled volatile gases reflect the physical
condition of a patient, a breath analysis allows one to recognize an infectious disease in an organ or even to identify a
tumor. One of the most prominent breath tests is the
13C-urea-breath test, applied to ascertain the presence of the
bacterium helicobacter pylori in the stomach wall as an indication of a gastric ulcer. In this contribution we present a
new optical analyzer that is based on photoacoustic spectroscopy and uses a DFB diode laser at 2.744 μm. The
concentration ratio of the CO2 isotopologues is determined by measuring the absorption on a 13CO2 line in comparison to
a 12CO2 line. In the specially selected spectral range the lines have similar strengths, although the concentrations differ
by a factor of 90. Therefore, the signals are well comparable. Due to an excellent signal-noise-ratio isotope variations of
less than 1% can be resolved as required for the breath test.
We present a new detection scheme for carbon dioxide(CO2) based on a custom-made room temperature distributed
feedback (DFB) diode laser at 2.7 μm, currently representing the laser with the highest emission wavelength of its kind.
The detector's especially compact and simple set-up is based on photoacoustic spectroscopy (PAS). This method makes
use of the transformation of absorbed modulated radiation into a sound wave. The sensor enables a very high detection
sensitivity for CO2 in the ppb range. Furthermore, the carefully selected spectral region as well as the narrow bandwidth
and wide tunability of the single-mode laser ensure an excellent selectivity. Even measurements of different CO2
isotopes can be easily performed. This could enable future applications of this spectroscopic sensor in medical
diagnostics (e.g. 13C-breath tests).
Development of new optical sensor technologies has a major impact on the progression of diagnostic methods. Specifically, the optical analysis of breath is an extraordinarily promising technique. Spectroscopic sensors for the non-invasive 13C-breath tests (the Urea Breath Test for detection of Helicobacter pylori is most prominent) are meanwhile well established. However, recent research and development go beyond gastroenterological applications. Sensitive and selective detection of certain volatile organic compounds (VOCs) in a patient's breath, could enable the diagnosis of diseases that are very difficult to diagnose with contemporary techniques. For instance, an appropriate VOC biomarker for early-stage bronchial carcinoma (lung cancer) is n-butane (C4H10). We present a new optical detection scheme for VOCs that employs an especially compact and simple set-up based on photoacoustic spectroscopy (PAS). This method makes use of the transformation of absorbed modulated radiation into a sound wave. Employing a wavelength-modulated distributed feedback (DFB) diode laser and taking advantage of acoustical resonances of the sample cell, we performed very sensitive and selective measurements on butane. A detection limit for butane in air in the ppb range was achieved. In subsequent research the sensitivity will be successively improved to match the requirements of the medical application. Upon optimization, our photoacoustic sensor has the potential to enable future breath tests for early-stage lung cancer diagnostics.
The development of new optical sensor technologies has a major impact on the progress of diagnostic methods. Of the permanently increasing number of non-invasive breath tests, the 13C-Urea Breath Test (UBT) for the detection of Helicobacter pylori is the most prominent. However, many recent developments, like the detection of cancer by breath test, go beyond gastroenterological applications. We present a new detection scheme for breath analysis that employs an especially compact and simple set-up. Photoacoustic Spectroscopy (PAS) represents an offset-free technique that allows for short absorption paths and small sample cells. Using a single-frequency diode laser and taking advantage of acoustical resonances of the sample cell, we performed extremely sensitive and selective measurements. The smart data processing method contributes to the extraordinary sensitivity and selectivity as well. Also, the reasonable acquisition cost and low operational cost make this detection scheme attractive for many biomedical applications. The experimental set-up and data processing method, together with exemplary isotope-selective measurements on carbon dioxide, are presented.